1. Field of the Invention
The present invention relates to a solder material containing no lead for soldering electric, electronic or mechanical components, and a device in which the solder material is used for bonding, and a manufacturing process for the device or apparatus using the solder material. More particularly, the invention relates to a tin-based solder material being suitable for a high-temperature solder which is used as a bonding material for manufacturing products which is significantly durable under increased temperature conditions, a device or apparatus produced using that solder material fur assembling, and a manufacturing process for that device using the solder material.
2. Related Art
In the current industries, soldering is widely used for bonding and assembling of various derives and apparatuses including electronic components and the like. For example, surface mounting process involves solder bonding for mounting electronic components including semiconductors, microprocessors, memories, resistors and the like on a printed circuit board.
The conventional solder materials which have been popularly used are of the eutectic tin/lead alloy type which is mainly composed of tin and lead. The theoretical eutectic point of tin/lead alloy is 183xc2x0 C., which is lower than the temperature where most of thermoset resins start turning to a gaseous form. Accordingly, such tin/lead eutectic solder materials have an advantage that their increased temperature for bonding the components may hardly give damage to printed circuit boards and the like on when the soldering is carried out. It is hence known in the electronic industries that tin/lead eutectic solders are primary materials for assembling and soldering the components to produce an electronic device, On the other hand, high-temperature solder materials such as Pb-5%Sn are favorably used for manufacturing a semiconductor device, e.g. a power transistor, which is commonly loaded with high voltage and current and possibly generates a considerable amount of heat so that they offer higher resistance to heat at the joints.
However, the issue of environmental protection from industrial wastes has been under consideration for recent years. The conventional solder materials equally provide a drawback that lead contained in the electronic devices may be eluted as lead ions and accumulated in the ground. In order to solve the above problems, improved soldering techniques with the use of soldering materials which contain no lead is needed.
However, newly proposed soldering materials where lead is replaced by one or more metals fail to exhibit satisfactory levels of the soldering characteristics, such as wetting property, soldering temperature, physical strength and cost effectiveness. Therefore, they can hardly be used for general products throughout the relevant industries, but may only be admitted for use in specific applications.
The inventors of the present application have proposed the use of a tin/zinc solder under particular controlled conditions, which consists mainly of generally available metals but contains no lead thus eliminating the above drawback of environmental pollution (See Japanese Patent Application Laid-open No. 8-243782). Since the tin/zinc eutectic composition is low in the melting point, it can favorably be used as a low-temperature solder material equivalent to the conventional tin/lead solders provided that the wetting property attributed to the tin/Zinc solder is exhibited. This may indicate the introduction of a qualified low melting-point solder without using lead.
However, the introduction of improved high-temperature solder is not yet feasible.
Proposed in Japanese Patent Application Laid-open No. 1-172352 is a Zn/Al/Mg-based solder which contains no lead and may replace the Pb-5% Sn solder as a conventional high-temperature solder material. However, this material is rather low in the processability and also poor in the wetting property due to the composition of easily oxidizable elements, hence being unfavorable for practical use.
On the other hand, tin/copper-based solders have been attempted for use in practice. However, it has developed that a xcex7 phase of intermetallic compound between tin and copper produces, thus deteriorating the joint with copper members and declining its physical strength.
It is, therefore, an object of the present invention to provide a lead-free high-temperature solder which consists of generally available, less expensive materials and is suited for soldering at a higher range of temperature.
It is another object of the present invention to provide an assembly or a device which is joined and/or assembled by soldering with the lead-free high-temperature solder made of generally available materials, thus having a higher resistance to heat.
The inventors of the present application have conducted a series of studies for developing an improved technique of soldering with a tin/zinc-based solder which contains no lead and consists mainly of generally available materials. As a result, it is proved that the high-temperature solder is implemented by a composition containing tin as the base material with zinc and silver, or a tin-based composition containing germanium or aluminum.
In order to achieve the above-mentioned object, a solder material according to the present invention comprises: tin, zinc and silver, wherein the ratio of tin to zinc is within a range of 97/3 to 79/21 by weight, and the ratio of the sum of tin and zinc to sliver is within a range of 88/12 to 50/50 by weight.
According to another aspect, a solder material of the present invention comprises: tin, zinc and silver, wherein the ratio of tin to zinc is within a range of 70/30 to 5/95 by weight, and the ratio of silver to the sum of tin, zinc and silver is 15% by weight or less.
According to further aspect, a solder material of the present invention consists essentially of 0.01 to 2% by weight of a metal element selected from the group consisting of germanium and aluminum, and the balance tin.
According to further aspect, a high temperature solder material for use in a power device of the present invention comprises tin and zinc, wherein the ratio of tin to zinc is 70/:30 to 80/20.
An electric or electronic device according to the present invention comprises parts which are joined with a solder material, and the solder material comprising either of the above-described solder materials.
A process for manufacturing an electric or electronic device according to the present invention, comprises: soldering with a first solder material at a first temperature; and soldering later than soldering with the first solder material with a second solder material at a second temperature which is lower than the first temperature, wherein the first solder material comprises one of the above-described solder materials.